Wheel bearing apparatus is used to freely rotationally supporting a wheel hub for mounting a wheel, via a rolling bearing, for driving wheels and driven wheels. For structural reasons, an inner ring rotation type is generally used for a driving wheel and both inner ring rotation and outer ring rotation types for a driven wheel. Double row angular ball bearings are widely used in such a bearing apparatus. This is due to the fact that it has a desirable bearing rigidity, high durability against misalignment and small rotation torque superior, for fuel consumption. On the other hand, double row tapered roller bearings are used for heavy weight vehicles such as off-road cars or trucks.
Vehicle wheel bearing apparatus is broadly classified into a number of structures. A first generation type has a wheel bearing with double row angular contact ball bearings fit between a knuckle, forming part of a suspension, and a wheel hub. A second generation type has a body mounting flange or a wheel mounting flange directly formed on the outer circumference of an outer member. A third generation type has one of the inner raceway surfaces directly formed on the outer circumference of the wheel hub. A fourth generation type has the inner raceway surfaces directly formed on the outer circumferences of the wheel hub and the constant velocity universal joint.
The wheel bearing apparatus shown in FIG. 22 is a fourth generation type. It is superior for its light weight and small size. It includes a unit of a wheel hub 100, a double row rolling bearing 101, and a constant velocity universal joint 102. The double row rolling bearing 101 has an outer member 103, an inner member 104, and a plurality of balls 105 and tapered rollers 106 contained between the outer and inner members 103, 104. In the descriptions below, the term “outer side” defines a side positioned outside of a vehicle body (left-hand side in drawings). The term “inner side” defines a side that is positioned inside of the vehicle body (right-hand side in drawings) when the bearing apparatus is mounted on the vehicle body.
The outer member 103 is formed with the body mounting flange 103c on its outer circumference. The body mounting flange 103c is mounted on a knuckle (not shown) forming part of a suspension of the vehicle. The outer member inner circumference has double row outer raceway surfaces 103a, 103b. A diameter of the outer side outer raceway surface 103a is set smaller than that of the inner side outer raceway surface 103b. The inner member 104 has a wheel hub 100, an outer joint member 108 of the constant velocity universal joint 102 integrally formed with the wheel hub 100, and a separate inner ring 107 press-fit onto the outer joint member 108.
The wheel hub 100 is formed on one end with a wheel mounting flange 100b to mount a wheel (not shown). Its outer circumference has an inner raceway surface 100a arranged opposite to the outer side outer raceway surface 103a of the double row outer raceway surfaces 103a, 103b. The outer circumference of the inner ring 107 has an inner raceway surface 107a arranged opposite to the inner side outer raceway surface 103b of the double row outer raceway surfaces 103a, 103b. 
The constant velocity universal joint 102 has the outer joint member 108. It includes a cup-shaped mouth portion 109 and a shoulder portion 110 that forms a bottom portion of the mouth portion 109. The inner circumference of the outer joint member 108 is formed with curved track grooves 108a. The inner ring 107 is press-fit onto the outer circumference of the mouth portion 109 and axially immovably secured by a snap ring 111.
The plurality of balls 105 are freely rollably contained between the outer side outer and inner raceway surfaces 103a, 100a. The plurality of tapered rollers 106 are freely rollably contained between the inner side outer and inner raceway surfaces 103b, 107a. The pitch circle diameter of the outer side balls 105 is set smaller than the inner side tapered rollers 106. This enables the fundamental rated load of the inner side rolling elements, to which a larger load is applied than a load applied to the outer side rolling elements, to be larger than the fundamental rated load of the outer side rolling elements. Thus, this enables the life of the outer side and inner side rolling elements to be substantially the same as each other and to obtain a smart design (see e.g. Japanese Laid-open Patent publication No. 91308/1999).
In such a wheel bearing apparatus, since the inner ring 107 is secured on the mouth portion 109 of the outer joint member 108, the size of the apparatus can be reduced in its axial direction. However, since the outer diameter of the outer member 103 is enlarged, not only is the reduction of the weight of the wheel bearing apparatus hampered but also its design modification of related parts, such as a knuckle, is required. To solve such a problem, the wheel bearing apparatus shown in FIG. 23 has been proposed.
This wheel bearing apparatus is formed by a double row angular contact ball bearing with an outer member 112. The outer member 112 is formed with a body mounting flange 112c on its outer circumference. The body mounting flange 112c is to be mounted on a knuckle (not shown) of a vehicle. The outer member inner circumference 112 has double row outer raceway surfaces 112a, 112b. An inner member 116 includes a wheel hub 114 formed on its one end with a wheel mounting flange 113 to mount a wheel (not shown). Its outer circumference has an inner raceway surface 114a arranged opposite to the outer side outer raceway surface 112a of double row outer raceway surfaces 112a, 112b. A cylindrical portion 114b axially extends from the inner raceway surface 114a. An inner ring 115 has an inner raceway surface formed on its outer circumference. The inner raceway surface 115a is arranged opposite to the inner side outer raceway surface 112b of the double row outer raceway surfaces 112a, 112b. Double row balls 117, 118 are freely rollably contained between the outer raceway surfaces and inner raceway surfaces. Cages 119, 120 freely rollably hold the double row balls 117, 118.
The inner ring 115 is axially secured by a caulked portion 114c. It is formed by plastically deforming the end of the cylindrical portion 114b of the wheel hub 114 radially outward. Seals 121, 122 are mounted within annular openings formed between the outer member 112 and the inner member 116. The seals prevent leakage of lubricating grease sealed within the bearing and rain water or dusts from entering into the bearing from the outside.
In this wheel bearing apparatus, a pitch circle diameter D1 of the outer side row of balls 117 is set larger than a pitch circle diameter D2 of the inner side row of balls 118. Accordingly, the diameter of the inner raceway surface 114a of the wheel hub 114 is larger than that of the inner raceway surface 115a of the inner ring 115. The diameter of the outer side outer raceway surface 112a of the outer member 112 is larger than that of the inner side outer raceway surface 112b. In addition, the number of the outer side balls 117 is larger than the number of inner side balls 118. By setting the relation between the pitch circle diameters D1, D2 as D1>D2, it is possible to increase the rigidity of the wheel bearing apparatus not only in the case of running in a straight way but also in case of running in a curved way. Thus, this extends the life of the wheel bearing apparatus (see e.g. Japanese Laid-open Patent publication No. 108449/2004).